The present invention relates generally to the field of presses, and, more particularly, to the field of press brakes which are intended to form or stamp relatively elongate portions of sheet material workpieces, such as sheet metal. In particular, the present invention relates to such presses which are actuated by fluidic actuators, such as pneumatic pistons and cylinders. In the prior art, presses actuated by various means, including pneumatic pistons and cylinders, have utilized punch and die sets to perform work on a workpiece. Pneumatically actuated presses have generally been limited to light duty work since pneumatic systems are limited in capacity. Some examples of prior art presses are illustrated in U.S. Pat. Nos. 1,038,934, 1,488,562, 2,241,794 and 3,230,812.
In U.S. Pat. No. 3,968,714, dated July 13, 1976, a shear is disclosed comprising, in part, a hydraulic power cylinder and a lever for drivingly connecting the power cylinder to a movable blade, the lever being pivotally mounted upon the frame to provide oppositely extending lever portions, one pivotally connected to the movable blade and the other pivotally connected to the ram of the power cylinder. This patent also discloses a roller journal mounted upon brackets to extend across the frame with the brackets selectively adjustably movable to position the roller, and springs for yieldably urging the movable blade against the roller.
In U.S. Pat. No. 3,196,727 (Pray) a similar hydraulic shear is disclosed, wherein a hydraulic cylinder mechanism may be utilized to oscillate a movable shear arm. Active portions of the stationary shear arm and the movable shear arm support the cutting blades which are positioned to overhang one of the sides of a tank structure which forms the supporting frame of the shear mechanism. More recently, in the patents and patent applications referred to above, particularly as shown in U.S. Pat. Nos. 4,004,480; 4,080,860 and 3,690,207, each of which patents is hereby incorporated by reference, significant advances have been made in the art of amplifying forces provided by pneumatic or hydraulic actuators through level-type amplifying means which apply forces to movable punch portions while minimizing shearing (transverse) forces applied by the amplification means to the punch portion.
Unique difficulties are encountered in the field of press brakes, particularly since such brakes typically are used to stamp or form relatively long portions of sheet material. By way of example, such press brakes may be used to form lengths of gutter material, lengths of architectural metal work, such as cornices, and other sheet metal objects which typically are formed into lengths which have relatively uniform cross-sections from one end to the other. A major difficulty which is encountered in carrying out forming operations on lengths of sheet material, however, is that differential resistances which are encountered from one end of the die to the other interfere with the forming operation. These differing resistances result from a number of variables, such as punch and die set tolerances, sheet metal thickness variations, wear, the presence of foreign materials, etc. While the variations in encountered resistance from one end of the die set to the other may be slight, the effects of such differential resistances on the finished workpiece can be substantial, since complete closure of the punch and die set with uniform pressure along its entire length should result in order to ensure a uniform bending or stamping operation. Slight differences from end to end in force and/or closure can result in substantial differences in the finished product. Additionally, differential resistances along the length of the punch and die set tend to impart slight rotational forces on the moving ram of the press brake which can tend to cause that ram to bind along its track, thereby amplifying the problem and further impairing the quality of the finished product.